For purposes of clarity and consistency, the following terms as used throughout this text and the appended claims should be interpreted as follows:
The phrase “substantially planar” should be construed as referring to a substrate in the (approximate) form of a sheet, plate, leaf, wafer, platen, etc. Such a substrate will generally be (substantially) flat in form, and present two opposed major surfaces separated by a relatively thin intervening “sidewall”, though as will be appreciated, a substantially planar substrate may include some structure such as microcircuitry layers that have some degree of relief.
The phrase “semiconductor substrate” should be broadly interpreted as encompassing any substrate on which a semiconductor device or other integrated device is manufactured. Such substrates may, for example, comprise silicon or germanium wafers (of various diameters), and/or wafers of compound substances such as InAs, InSb, InP, GaSb, GaP or GaAs. The term also encompasses non-semiconductor materials (such as sapphire) on which one or more layers of semiconductor material have been deposited, e.g. as in the manufacture of LEDs. The semiconductor device or other integrated device concerned may, for example, be an integrated circuit, (passive) electronic component, opto-electronic component, biological chip, MEMS device, etc. Such devices will generally be manufactured in large numbers on a given substrate, and will typically be laid out in a matrix arrangement on at least one of said major surfaces.
The term “scribeline” (also sometimes referred to as a “scribelane”) should be interpreted as referring to a (real or abstract) line extending along a major surface of a substrate, along which line the substrate is to be scribed. In the specific case of a semiconductor substrate, a scribeline will generally lie in a “street” (dicing street) that extends between neighboring/adjacent/opposed rows of integrated devices on the substrate, along which street the substrate is to be “diced” so as to allow (ultimate) separation of the devices in question. Such a procedure is often referred to as “singulation”. It should be noted that scribelines on the target surface may be arranged in regular and/or non-regular (repetitive) configurations. For example, some wafers may comprise a regular matrix of identical integrated devices separated from one another by scribelines forming a regular orthogonal network. On the other hand, other wafers may comprise devices of different sizes, and/or located at non-regular pitches with respect to one another, implying a correspondingly irregular configuration of scribelines. The arrangement of such scribelines does not necessarily have to be orthogonal.
The term “groove” refers to a scribe (gouge, furrow, channel) that does not penetrate through the full thickness of the substrate in which it is created, i.e. creation of the groove does not directly cause severance of the substrate (in the Z direction). Substrate singulation involving such grooving is thus necessarily a multi-step procedure (as opposed to single-step singulation, in which the substrate is cut/severed through its full depth in a single operation). In multi-step singulation, one or more follow-up procedures are used to finish off the severing process, such as additional radiative scribing, mechanical sawing/cutting, etc. along the previously created groove.
The phrase “laser scribing head” refers to an optical assembly that can be used to produce and direct scribing laser radiation in a laser scribing apparatus/tool. Such a head will generally comprise at least one laser source and associated imaging/focusing optics. It may also comprise one or more ancillary components, such as beam splitters, diffractive optical elements or filters (for example), for performing specific processing operations on said laser radiation. Laser scribing apparatus is well known in the art of wafer singulation: see, for example, U.S. Pat. No. 5,922,224 and U.S. Pat. No. 7,947,920, which are incorporated herein by reference.
These points will be discussed in more detail below.
Grooving of semiconductor substrates using a laser scribing apparatus is a well-known and widely applied technique in the semiconductor manufacturing industry. It is applied, in particular, on semiconductor substrates comprising a relatively brittle and/or poorly adhered top layer, e.g. as in the case of a so-called “low-k” dielectric top layer (which has a relatively low dielectric constant (k) relative to silicon dioxide). Such problematic top layers (which are typically of the order of about 1-10 microns thick) are difficult to scribe using mechanical means, which tend to cause unacceptable cracking and/or de-lamination of the top layer in (external) regions bordering the intended scribe. However, such top layers can be much more satisfactorily ablated using a radiative scribing tool. Consequently, substrates carrying such a layer are conventionally first grooved using a laser scribing apparatus, before being singulated at a later juncture using a mechanical tool. An added advantage is that, in addition to neatly scribing the problematic top layer, radiative grooving can also remove certain surfacial metal structures in the dicing street, such as so-called TEGs (Test Element Groups); this can help improve the useful lifetime of blades used for subsequent mechanical singulation. The depth of a radiative groove is typically of the order of about 15 μm (for instance). Because (saw) blades used for follow-up singulation tend to be relatively thick (e.g. about 50 μm wide), the groove itself will have to be correspondingly relatively wide, e.g. of the order of about 60 μm (for instance).
However, such use of radiative grooving as a prelude to mechanical singulation can cause certain problems. In particular, since the (ablative) radiative grooving process is thermal in nature, it will cause the generation of heat within the groove, but also in a peripheral zone running along the outside edges of the groove. This so-called Heat-Affected Zone (HAZ) adjacent to the groove is a region where temperatures are generally too low to cause ablation, but nevertheless high enough to cause other, unwanted thermal effects, such as burning, melting, discoloration or a change in other physical/chemical properties (such as dielectric constant, impedance, crystalline phase, etc.).
To avoid this HAZ issue, one can increase the width of the dicing street, so that devices located along the groove are moved further away from the HAZ. However, a wider dicing street entails a loss of available device area (“real estate”) on the substrate, leading to an increase in cost per device. This is highly undesirable.